Answer:
Because each the cells would have different functions on different organisms.
Step-by-step explanation:
Bacteria cells are usually prokaryotic which means that it is only composed of one cell. The single cell already has everything it needs so therefore, it isn't as complex as plant and animal cells.
Plants are autotrophs and produce their own food through photosynthesis. Plant cells would have a large vacuole, cell wall, chloroplasts, unlike animal cells.
Animal cells have all the cell organs that plant cells except a large vacuole, cell wall, and chloroplasts. Animal cells also have lysosomes in which plant cells don't.